Organic light emitting diode with light-scattering layer with nano structure and air gaps

ABSTRACT

Provided is an organic light emitting diodes (OLED) and method of manufacturing the OLED. The OLED includes: a substrate; a light scattering layer having an uneven shape on the substrate; a transparent electrode film provided directly on and in contact with the light scattering layer; an organic light emitting layer on the transparent electrode film; and an electrode on the organic light emitting layer. The method of manufacturing the OLED includes: disposing a light scattering layer on a substrate; providing a transparent electrode film on the light scattering layer; and transferring the transparent electrode film to be directly on and in contact with the light scattering layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This U.S. non-provisional patent application claims priority under 35U.S.C. §119 of Korean Patent Application No. 10-2014-0061352, filed onMay 22, 2014, the entire contents of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

The present invention disclosed herein relates to an organic lightemitting diode and a method of manufacturing the same.

An organic light emitting diode (OLED) is a self light emitting elementthat electrically excites an organic light emitting substance to emitlight. The OLED includes a substrate, a first electrode, a secondelectrode, and an organic light emitting layer disposed between thefirst electrode and the second electrode. The organic light emittinglayer generates light by the combination of holes and electrons suppliedfrom the first and second electrodes. The OLED is a device emittinglight for itself and has a wide viewing angle, a rapid response speedand high colorgamut. The OLED is being applied to a display device. Inrecent, a research on applying the OLED to lighting is being conducted.

The OLED includes components, such as a substrate, a light scatteringlayer and an organic light emitting layer that are stacked. Lightgenerated at the organic light emitting layer is visually perceived onlywhen the light passes through the interface between different kinds ofsubstances and substance layers having different refractive indexes. Dueto the interface between the different kinds of substances and thedifferent refractive indexes, generated light is optically guided orexperiences total internal reflection. Because of such an opticalstructure, most of the light generated by the OLED is lost. Only a smallfraction (up to about 20%) of the generated light is generated from anelement and visually perceived from the outside.

SUMMARY OF THE INVENTION

The present invention provides an organic light emitting diode andmethod of manufacturing the same that increase light extractionefficiency.

Embodiments of the present invention provide organic light emittingdiodes (OLED) including: a substrate; a light scattering layer having anuneven shape on the substrate; a transparent electrode film provideddirectly on and in contact with the light scattering layer; an organiclight emitting layer on the transparent electrode film; and an electrodeon the organic light emitting layer.

In some embodiments, the light scattering layer may include nanostructures and air gaps between the nano structures. Widths of the nanostructures may be about 50 nm to about 3000 nm and distances between thenano structures may be about 50 nm to about 3000 nm.

In other embodiments, the transparent electrode film may include atleast one of conducting polymer, conductive oxide, carbon-basedsubstance and metallic substance. The conducting polymer may include atleast one of poly (3,4-ethylenedioxythiophene), poly(4-styrenesulfonate), polyacetylene, poly (p-Phenylene), polythiophene,poly (ethylenedioxythiophene), polypyrrole, poly (p-phenylene vinylene),poly (thienylene vinylene), polyaniline, polyisothianaphthene, and poly(p-phenylene sulfide). The conductive oxide may include at least one ofindium tin oxide (ITO) and indium zinc oxide (IZO).

In still other embodiments, the transparent electrode film may includeat least one of graphene, molybdenum disulfide (MoS₂) and tungstensulfide (WS₂).

In other embodiments of the present invention, methods of manufacturingan OLED include: forming a light scattering layer on a substrate;providing a transparent electrode film on the light scattering layer;and transferring the transparent electrode film to be directly on and incontact with the light scattering layer.

In some embodiments, the transparent electrode film may include at leastone of graphene, molybdenum disulfide (MoS₂) and tungsten sulfide (WS₂).

In other embodiments, the transferring of the transparent electrode filmmay include providing the transparent electrode film directly on and incontact with the light scattering layer and performing heat treatment.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the present invention, and are incorporated in andconstitute a part of this specification. The drawings illustrateexemplary embodiments of the present invention and, together with thedescription, serve to explain principles of the present invention. Inthe drawings:

FIG. 1 is a cross-sectional view of an organic light-emitting diode(OLED) according to an embodiment of the present invention; and

FIGS. 2 to 7 are cross-sectional views of a method of manufacturing anOLED according to an embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The effects and features of the present invention, and implementationmethods thereof will be clarified through following embodiments to bedescribed in detail with reference to the accompanying drawings. Thepresent invention may, however, be embodied in different forms andshould not be construed as limited to the embodiments set forth herein.Rather, these embodiments are provided so that this disclosure isthorough and complete and fully conveys the scope of the presentinvention to a person skilled in the art to which the present inventionpertains. Further, the present invention is only defined by scopes ofclaims. The same reference numerals throughout the disclosure refer tothe same components.

Also, embodiments in the present disclosure are described with referenceto ideal, exemplary cross sectional views and/or plan views of thepresent invention. The thicknesses of layers and regions in the drawingsare exaggerated for the effective description of technical content.Thus, the forms of exemplary views may vary depending on manufacturingtechnologies and/or tolerances. Thus, embodiments of the presentinvention are not limited to shown specific forms and also includevariations in form produced according to manufacturing processes. Forexample, an etch region shown as a rectangular shape may have a roundshape or a shape having a certain curvature. Thus, regions illustratedin the drawings are exemplary, and the shapes of the regions illustratedin the drawings are intended to illustrate the specific shapes of theregions of elements and not to limit the scope of the present invention.

FIG. 1 is a cross-sectional view of an organic light-emitting diode(OLED) according to an embodiment of the present invention.

Referring to FIG. 1, a light scattering layer 200, a transparentelectrode film 300, an organic light emitting layer 400, an electrode500, and a protective layer 600 may be sequentially disposed on asubstrate 100.

The substrate 100 may transmit light. The substrate 100 may be aninorganic substrate. For example, the substrate 100 may include at leastone of silicon oxide (SiO₂), silicon nitride (SiN), silicon (Si), andtitanium oxide (TiO₂). The substrate 100 may be an organic substrate.For example, the substrate 100 may include at least one of polyimide),polyethylene terephthalate (PET) and/or polyacrylate.

The light scattering layer 200 may be provided on the substrate 100. Thelight scattering layer 200 may include nano structures 230. The nanostructures 230 may be about 50 nm to about 3000 nm. The distance betweenthe nano structures 230 may be about 50 nm to about 3000 nm and theremay be irregular widths and distances. For example, the nano structures230 may have a circle shape, an ellipse shape, a capsule shape, or acircular concave shape. The nano structures 230 may include at least oneof transparent materials. For example, the nano structures 230 mayinclude at least one of oxide such as SiO₂, SnO₂, TiO₂, TiO₂—SiO₂, ZrO₂,Al₂O₃, HfO₂, In₂O₃, or ITO, nitride such as SiNx, and a resin such as apolyethylene, polyacrylate, or polyvinyl chloride (PVC) resin, apolyvinylpyrrolidone resin, or a polyimide, polystyrene, or epoxy resin.The light scattering layer 200 may further include an air gap 240between the nano structures 230.

The irregularly uneven structure of the light scattering layer 200 maywork as a light scattering element. The irregularly uneven structure ofthe light scattering layer 200 has an irregular shape, size (height ordiameter) and/or arrangement. The light scattering layer 200 may performscattering, reflection, scattered refraction and diffraction on incidentlight without dependence on a specific wavelength. The light scatteringlayer 200 may be effective in enhancing light extraction efficiency.Thus, it is possible to enhance the light extraction efficiency of theOLED 1. As another example, the light scattering layer 200 may haveregular structure.

The transparent electrode film 300 is located on the nano structures230. The transparent electrode film 300 may be an anode electrode. Thetransparent electrode film 300 may receive a voltage from the outside tosupply a hole to the organic light emitting layer 400. The transparentelectrode film 300 includes at least one of oxide-based, polymer-based,carbon-based substance, a metallic substance and synthesized polymer.Conducting polymer may includepoly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS),polyacetylene, poly(p-phenylene), polythiophene,poly(ethylenedioxythiophene), polypyrrole, poly(p-phenylene vinylene),poly(thienylene vinylene), polyaniline, polyisothianaphthene, andpoly(p-phenylene sulfide). Transparent conductive oxide (TCO) mayinclude indium tin oxide (ITO) and indium zinc oxide ((IZO). Thetransparent electrode film 300 may include a transparent electrode suchas graphene, molybdenum disulfide (MoS₂) and tungsten sulfide (WS₂) thatis 2-dimensionally formed.

The organic light emitting layer 400 may be provided on the transparentelectrode film 300. The organic light emitting layer 400 may generatelight through the recombination of holes supplied from the transparentelectrode film 300 and electrons supplied from the electrode 500. It isalso possible to further include a secondary layer (not shown)increasing the light emitting efficiency of the organic light emittinglayer 400. The secondary layer may include at least one of a holeinjecting layer, a hole transfer layer, an electron transfer layer andan electron injecting layer. The organic light emitting layer 400 mayinclude at least one of organic light emitting substances. For example,the organic light emitting layer 400 may include at least one of apolyfluorene derivative, a (poly) paraphenylenevinylene derivative, apolyphenylene derivative, a polyvinylcarbazole derivative, apolythiophene derivative, an anthracene derivative, a butadienederivative, a tetracene derivative, a distyrylarylene derivative, abenzazole derivative and carbazole. According to other embodiments, theorganic light emitting layer 400 may be an organic light emittingsubstance including a dopant. For example, the dopant may include atleast one of xanthene, perylene, cumarine, rhodamine, rubrene,dicyanomethylenepyran, thiopyran, (thia) pyrilium, a periflanthenederivative, an indenoperylene derivative, carbostyryl, nile red, andquinacridone. The organic light emitting substance may include at leastone of a polyfluorene derivative, a (poly) paraphenylenevinylenederivative, a polyphenylene derivative, a polyvinylcarbazole derivative,a polythiophene derivative, an anthracene derivative, a butadienederivative, a tetracene derivative, a distyrylarylene derivative, abenzazole derivative and carbazole.

The electrode 500 may be provided on the organic light emitting layer400. The electrode 500 may be a cathode. The electrode 500 may receive avoltage from the outside to supply an electron to the organic lightemitting layer 400. The electrode 500 may transmit light generated fromthe organic light emitting layer 400 or reflect the light to thetransparent electrode film 300. The electrode 500 may include aconductive material. The electrode 500 may be a metallic or opticallytransparent conductive material. For example, metal may be aluminum(Al), silver (Ag), magnesium (Mg), molybdenum (Mo) or alloy thereof. Thetransparent electrode film 500 may include a transparent electrode suchas graphene, molybdenum disulfide (MoS₂) and tungsten sulfide (WS₂) thatis 2-dimensionally formed. The optically transparent conductive materialmay include a metallic thin film. The wavelength of light passingthrough the thin film may vary depending on the thickness of the thinfilm.

The protective layer 600 may be provided on the electrode 500. Theprotective layer 600 may be a sealed protective layer and a packagedglass plate. The protective layer 600 may include an air blockingmaterial. The protective layer 600 may include a transparent material.The protective layer 600 protects the organic light emitting layer 400.The protective layer 600 may include organic film and 2-dimesionalmaterial such as molybdenum disulfide (MoS₂) and tungsten sulfide (WS₂)

FIGS. 2 to 7 are cross-sectional views of a manufacturing method of anOLED according to an embodiment of the present invention.

Referring to FIG. 2, a light-scattering medium layer 210 and a metallicthin film layer 220 are sequentially formed on the substrate 100. Thesubstrate 100 may be washed before forming the light-scattering mediumlayer 210. Washing may be performed by distilled water, organic solvent,base solution and acid solution. The light-scattering medium layer 210may be formed by deposition. For example, the light-scattering mediumlayer 210 may be formed by sputtering, chemical vapor deposition (CVD),E-beam evaporation, thermal evaporation and/or atomic layer deposition(ALD). The light-scattering medium layer 210 may include at least one ofoxide such as SiO₂, SnO₂, TiO₂, TiO₂—SiO₂, ZrO₂, Al₂O₃, HfO₂, In₂O₃, orITO, nitride such as SiNx, and a resin such as a polyethylene,polyacrylate, or polyvinyl chloride (PVC) resin, a polyvinylpyrrolidone(PVP) resin, or a polyamide, polystyrene, or epoxy resin. Thelight-scattering medium layer 210 may include a substance having thesame or a higher refractive index than the substrate 100. According toother embodiments, The light-scattering medium layer 210 may be omitted.For example, the light-scattering medium layer 210 may be formed to havea thickness of about 50 nm to about 1000 nm.

The metallic thin film layer 220 may be formed on the light-scatteringmedium layer 210. The metallic thin film layer 220 may be formed bydeposition and coating. For example, the metallic thin film layer 220may be formed by sputtering, chemical vapor deposition (CVD), E-beamevaporation, thermal evaporation and atomic layer deposition (ALD). Themetallic thin film layer 220 may include a material resistant to dryetching. For example, the metallic thin film layer 220 may include atleast one of metal (e.g., platinum (Pt), gold (Au), silver (Ag), copper(Cu), nickel (Ni), chrome (Cr), tungsten (W), zinc (Zn), tin (Sn),titanium (Ti), zirconium (Zr), aluminum (Al), and/or combinationsthereof), photoresist (e.g., poly (methyl methacrylate), (PMMA), poly(dimethylglutarimide (PMGI), or SU-8), a ceramic material (e.g., Al2O3)and/or an organic compound. When the thickness of the metallic thin filmlayer 220 is thin, the metallic thin film layer 220 may be deposited inan island form without forming a layer. For example, the metallic thinfilm layer 220 may be formed to have a thickness of about 10 nm to about100 nm.

Referring to FIG. 3, an etching mask 225 is formed. As an example, theetching mask 225 may be formed through thermal treatment on the metallicthin film layer 220. The etching mask 225 has an irregular pattern bydewetting. The dewetting means having an irregular pattern partiallyconcave or convex in a state in which a substance having a dewettingproperty is uniformly applied. The etching mask 225 may expose a portionof the light-scattering medium layer 210. For a thermal treatmentprocess, an oven or hot plate is used. The thermal treatment process maybe performed by thermal annealing or rapid thermal annealing (RTA). Thethermal treatment process may be performed at a point lower than orequal to a softening point of the substrate 100. For example, thethermal treatment may be performed at room temperature to a temperatureof 250° C. The etching mask 225 may have an irregular size andarrangement. The average diameter and thickness of the etching mask 225may be adjusted. For example, the etching mask 225 may have a size ofabout 100 nm to about 1000 nm. The etching mask 225 may have a thicknessof about 10 nm to about 500 nm.

Referring to FIG. 4, the nano structure 230 may be formed through a dryetching process using a reactive ion etching (RIE) or a inductivelycoupled plasma (ICP) by the etching mask 225 as an etch mask. Thelight-scattering medium layer 210 exposed by the etching mask 225 maybecome the nano structure 230 having an irregular pattern by etching.For example, the cross sections of the nano structures 230 may be inquadrilateral, trapezoidal, and circular shapes.

As another example, the nanostructure 230 may be formed through animprint lithography method. After manufacturing a mold having the shapeof the nano structure 230, it is possible to form the nano structure 230by applying heat and pressure to a polymer layer coated on thesubstrate.

As still another example, the substrate 100 is coated with a bead ornano wire having a higher etching selectivity ratio than the substrate100 or the light-scattering medium layer 210. The substrate 100 isetched by using a coated bead or nano wire as an etching mask. It ispossible to form the nano structure 230 by removing the etching mask.

Referring to FIG. 5, the etching mask 225 may be removed. The etchingmask 225 may be removed by the acid. For example, the acid may includenitric acid (HNO₃), sulfuric acid (H₂SO₄), aquaregia (HCl:HNO₃), andphosphoric acid (H₃PO₄). It is possible to remove the etching maskwithout destroying the nano structure 230 by using the acid.

Referring to FIG. 6, the transparent electrode film 300 is transferredonto the nano structure 230. The transparent electrode film 300 ispositioned directly on and in contact with the nano structure 230. Thetransparent electrode film 300 is transferred through thermal treatment.By the forming of the transparent electrode film 300, an air gap 240 isformed in the light scattering layer 200. Planarization is performed bythe direct transferring of the transparent electrode film 300 onto thenano structure 230 without a planarization layer process. It is possibleto decrease light loss due to a planarization layer by forming thetransparent electrode film 300 without the planarization layer. It ispossible to optimize a difference in refractive index by a lightextraction structure including the substrate 100, the transparentelectrode film 300, the nano structure 230 and the air gap 240 (having arefractive index of 1). Thus, it is possible to increase lightextraction efficiency.

The transparent electrode film 300 may be made from graphene. When thegraphene is used as the transparent electrode film 300, it is possibleto decrease light loss due to total reflection compared to whenconducting polymer and conductive oxide are used. Since a grapheneelectrode is formed as a thin film having a thickness of about 10 nm orless, it is possible to ignore an optical effect. The light generated atthe organic light emitting layer 400 is transmitted to the lightscattering layer 200 without optical loss. As such, it is possible tomaximize a light extraction effect by using the graphene.

Referring to FIG. 7, the organic light emitting layer 400, the electrode500, and the protective layer 600 may be sequentially formed on thetransparent electrode film 300. The organic light emitting layer 400 maybe formed by using a chemical vapor deposition (CVD), sputtering, E-beamevaporation technique or thermal evaporation technique. The organiclight emitting layer 400 may generate light through the recombination ofholes supplied from the transparent electrode film 300 and electronssupplied from the electrode 500. The light generated from the organiclight emitting layer 400 may be partially or totally reflected by thesubstrate 100 to be guided into the transparent electrode film 300 andthe organic light emitting layer 400. The light guided into the organiclight emitting layer 400 may not be emitted to the substrate 100.

The electrode 500 may be a cathode. The electrode 500 may receive avoltage from the outside to supply an electron to the organic lightemitting layer 400. The electrode 500 may transmit light generated fromthe organic light emitting layer 400 or reflect the light to thetransparent electrode film 300.

The protective layer 600 protects the organic light emitting layer 400.The protective layer 600 may be formed to cover the OLED 1.

According to an embodiment of the present invention, it is possible toincrease the light extraction efficiency of the OLED. Sinceplanarization is performed by the transferring of the transparentelectrode film onto the nano structure without a planarization layerprocess and the OLED is manufactured thereon, it is possible to decreaselight loss due to a planarization layer. It is possible to increase thelight extraction efficiency by the closer the distance between theorganic light emitting layer 400 and the light scattering layer 200.

According to an embodiment of the present invention, since thetransparent electrode film is manufactured by the transferring of atleast one of 2-dimensionally formed graphene, molybdenum disulfide(MoS₂) and tungsten sulfide (WS₂) onto the nano structure, it ispossible to decrease light loss due to total reflection compared to whenthe transparent electrode film is manufactured by the transferring ofconducting polymer and conductive oxide.

The above-disclosed subject matter is to be considered illustrative, andnot restrictive, and the appended claims are intended to cover all suchmodifications, enhancements, and other embodiments, which fall withinthe true spirit and scope of the present invention. Thus, to the maximumextent allowed by law, the scope of the present invention is to bedetermined by the broadest permissible interpretation of the followingclaims and their equivalents, and shall not be restricted or limited bythe foregoing detailed description.

What is claimed is:
 1. An organic light emitting diode (OLED)comprising: a substrate; a light scattering layer having an uneven shapeon the substrate; a transparent electrode film provided directly on andin contact with the light scattering layer; an organic light emittinglayer on the transparent electrode film; and an electrode on the organiclight emitting layer; wherein the light scattering layer comprises nanostructures and air gaps between the nano structures.
 2. The organiclight emitting diode (OLED) of claim 1, wherein widths of the nanostructures are about 50 nm to about 3000 nm and distances between thenano structures are about 50 nm to about 3000 nm.
 3. The organic lightemitting diode (OLED) of claim 1, wherein the transparent electrode filmcomprises at least one of conducting polymer, conductive oxide,carbon-based substance and metallic substance.
 4. The organic lightemitting diode (OLED) of claim 3, wherein the conducting polymercomprises at least one of poly (3,4-ethylenedioxythiophene), poly(4-styrenesulfonate), polyacetylene, poly (p-Phenylene), polythiophene,poly (ethylenedioxythiophene), polypyrrole, poly (p-phenylene vinylene),poly (thienylene vinylene), polyaniline, polyisothianaphthene, and poly(p-phenylene sulfide).
 5. The organic light emitting diode (OLED) ofclaim 3, wherein the conductive oxide comprises at least one of indiumtin oxide (ITO) and indium zinc oxide (IZO).
 6. The organic lightemitting diode (OLED) of claim 1, wherein the transparent electrode filmcomprises at least one of graphene, molybdenum disulfide (MoS₂) andtungsten sulfide (WS₂).